Charge Coupled Photodiodes utilize diffused photodiode sensors and incorporate CCD readout registers and output buffer amplifiers for low-noise signal extraction and thus combine the advantages of a Charge Coupled Device and a photodiode array. Two outputs from the array, designated even video and odd video, contain the useful information and these two outputs are combined in external video processing circuitry into one composite video circuit output.
Proper operation of the Charge Coupled Photodiode array requires that even and odd video output signals be balanced so that combination of these two signals gives a true composite video representation. In order to balance the video outputs, two individual bias voltages are applied to the odd input gate bias and even input gate bias terminals and are normally supplied through potentiometers to allow for optimum circuit performance. The usual adjustment procedure requires one bias voltage to be set to some nominal operating range and the other bias is adjusted to provide optimum balance between the odd and even outputs. However, temperature variations caused by equipment warmup and ambient temperature excursions require continual readjustment of the biasing circuits.